Method for providing deionized water with dynamic electrical resistivity

ABSTRACT

A method includes mixing a first deionized water (DI) water from a first pipe and a second DI water from a second pipe in a merging pipe that is in fluid communication with the first pipe and the second pipe. An electrical resistivity of the first DI water is different from an electrical resistivity of the second DI water. A mixture of the first DI water and the second DI water is applied from the merging pipe onto a wafer.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/627,472, filed on Jun. 20, 2017, now U.S. Pat. No. 10,464,032, issuedon Nov. 5, 2019, which claims priority to U.S. Provisional PatentApplication Ser. No. 62/487,512, filed on Apr. 20, 2017, all of whichare herein incorporated by reference in their entirety.

BACKGROUND

As semiconductor fabrication technologies are continually progressing,more and more challenges from defects on a wafer caused by accumulatedcharges have become important issue. For example, during anexposure/development process using an immersion lithography system,flowing water such as deionized (DI) water may introduce electrostaticcharges. The accumulated electrostatic charges cause particlecontamination such as particles adhering to surfaces of the immersionlithography system. The adhered particles may further migrate to asurface of the wafer and cause defects on the wafer and yielddegradations.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a schematic view showing a system for providing DI water witha dynamic electrical resistivity in accordance with some embodiments ofthe present disclosure.

FIG. 1B is a schematic view showing the system in FIG. 1A with dampershaving rotating angles.

FIG. 1C is a schematic view showing a system for providing DI water witha dynamic electrical resistivity in accordance with alternativeembodiments of the present disclosure.

FIG. 2A is a flow chart showing a method for providing DI water withdynamic electrical resistivity in accordance with some embodiments ofthe present disclosure.

FIG. 2B is a flow chart showing another control operation in the methodfor providing DI water with dynamic electrical resistivity in accordancewith some embodiments of the present disclosure.

FIG. 3A is a flow chart showing a method for providing DI water havingdynamic electrical resistivity is provided in accordance with someembodiments of the present disclosure.

FIG. 3B is a flowchart showing a control operation for providing DIwater with dynamic electrical resistivity in accordance with someembodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

The spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

Deionized (DI) water is applied in a semiconductor fabricating processfor various purposes such as developing, rinsing and/or cleaning inimmersion lithography process. The DI water having a predeterminedelectrical resistivity is usually used to avoid accumulation ofelectrostatic charges on a surface of a wafer during a semiconductorfabricating process. However, the traditional system and method can onlyprovide DI water with a fixed electrical resistivity regardless of arequirement of different electrical resistivities for different wafersor a same wafer in different intermediate stages of the semiconductorfabricating process to effectively reduce the accumulation ofelectrostatic charges. Therefore, a system and a method for providing DIwater with a dynamic electrical resistivity are provided to tackle theproblems described above.

Embodiments of the present disclosure are directed to providing a systemand a method of providing DI water with a dynamic electricalresistivity. Generally, the system includes DI water sources havingdifferent electrical resistivities and a flow control device (e.g. adamper or a flow control valve) in each of source pipes to mix DI waterhaving different electrical resistivities, so as to obtain (mixed) DIwater having a target electrical resistivity. The flow control devicemay be automatically controlled by a flow controller using a feedbackloop. Accordingly, the electrical resistivity of the DI water applied tothe semiconductor fabricating process is adjustable during theproceeding process, and the accumulation of electrostatic charges on thesurface of the wafer may be effectively reduced. The system and themethod of the present disclosure provide merits such as low costs,simplification and high performance of the semiconductor fabricatingprocess. A detailed description is provided by incorporating with FIG.1A through FIG. 3B.

Referring to FIG. 1A, FIG. 1A is a schematic view showing a system forproviding DI water with a dynamic electrical resistivity in accordancewith some embodiments of the present disclosure. As shown in FIG. 1A, asystem 100 includes DI water sources 110A and 110B, source pipes 120Aand 120B, flow control devices 130A and 130B, a merging pipe 140 and aflow controller 150. The source pipes 120A and 120B are respectivelyconnected to the DI water sources 110A and 110B in a one-to-one manner,and the flow control devices 130A and 130B are respectively disposed inthe source pipes 120A and 120B in a one-to-one manner. The merging pipe140 joins the source pipes 120A and 120B. The DI water sources 110A and110B have different electrical resistivities. For example, theelectrical resistivities of the DI water source 110A and 110B arerespectively 24 MΩ·cm and 12 MΩ·cm. The flow controller 150 isconfigured to control a flowrate in the source pipes 120A and 120B. Theflow controller 150 includes a resistivity sensor (not shown) disposedin the merging pipe 140 for detecting an actual electrical resistivityof the mixed DI water. In operation, DI water from the DI water sources110A and 110B enters the source pipes 120A and 120B, and thencollectively enters the merging pipe 140 to be ready for subsequentprocesses.

In some embodiments, the flow control devices 130 may be flow controlvalves (not shown), and the flow controller 150 is configured to adjustthe degrees of opening of the flow control valves. In other embodiments,the flow control devices 130 may be dampers with rotating angles, andthe flow controller 150 is configured to adjust the degrees of therotating angles. Referring to FIG. 1B, FIG. 1B illustrates a schematicview showing the system in FIG. 1A with dampers having rotating angles.Hereinafter, the flow control devices 130 A and 130B are referred to asa damper 130A having a rotating angle 132A and a damper 130B having arotating angle 132B, for convenience of explanation. In suchembodiments, the flow controller 150 is configured to adjust therotating angles 132A and 132B of the dampers 130A and 130B to controlthe flowrate of the DI water from the DI water sources 110A and 110B.That is, the greater the rotating angles, the greater the flow rates ofthe DI water. In some embodiments, the rotating angles 132A and 132B ofthe dampers 130A and 130B are in a range substantially from 0° to 90°,in which the rotating angles 132A is defined as an included anglebetween a direction perpendicular to a flow direction 170 and a topsurfaces 134A of the damper 130A, and the rotating angles 132B isdefined as an included angle between the direction perpendicular to theflow direction 170 and a top surfaces 134B of the damper 130B.Furthermore, the rotating angles 132A and 132B may not be 0° at the sametime, that is, at least one of the rotating angles 132A and 132B is not0°. In certain examples, the rotating angle 132A of the damper 130Ashown by a dotted-line is 0°, and the rotating angle 132B of the damper130B shown by the dotted-line is 90°. In other examples, the rotatingangle 132A of the dampers shown by a solid line is 90°, and the rotatingangle 132B of the damper 130B shown by the solid line is 0°.

Still referring to FIG. 1B, the flow controller 150 may include aresistivity sensor 152, in which the resistivity sensor 152 isconfigured to detect an electrical resistivity of the DI water in themerging pipe 140. In some embodiments, the flow controller 150 mayfurther include a driving module 154 and a judging module 156. Thedriving module 154 is at least signally connected to the dampers 130Aand 130B to control the rotating angles. The judging module 156 is atleast signally connected to the resistivity sensor 152, so as to comparean actual electricity resistivity of the DI water in the merging pipe140 with a target electricity resistivity. In addition, the judgingmodule 156 is also signally connected to the driving module 154.

As shown in FIG. 1A and FIG. 1B, in some embodiments, the system mayfurther include a calculating module 160. The calculating module 160 maybe signally connected to the driving module 154, in which thecalculating module 160 is configured to calculate the rotating angles132A and 132B of the damper 130A and 130B for obtaining the DI waterhaving the target electrical resistivity. In further embodiments, thecalculating module 160 performs a calculation according to the followingrelationship (1):

$\begin{matrix}{{R\left( {M\; {\Omega \cdot {cm}}} \right)} = \frac{\sum_{i = 1}^{n}{{Ri} \times {Ai}}}{\sum_{i = 1}^{n}{Ai}}} & (1)\end{matrix}$

where R stands for the target electrical resistivity; n stands for anumber of the DI water source; Ri stands for the electrical resistivityof DI water from the i^(th) DI water source; and Ai stands for therotating angle of the i^(th) damper.

In other embodiments, the driving module 154 and the dampers 130A and130B, the resistivity sensor 152 and the judging module 156, the drivingmodule 154 and the judging module 156, and/or the calculating module 160and the driving module 154 may be further electrically connected and/ orphysically connected.

In some embodiments, the resistivity sensor 152 detects an actualelectrical resistivity and sends a signal to the judging module 156, andthen the judging module 156 determines if the actual electricalresistivity is substantially equal to a target electrical resistivityand sends a signal to the driving module 154, the driving module 154controls the dampers 130A and 130B to adjust the rotating angles toadjust the flowrate of the DI water through the source pipes 120A and120B, and the DI water through the adjusted dampers may be detected bythe resistivity sensor 152, thereby forming a feedback loop forcontrolling the electrical resistivity of water dynamically, as shown inFIG. 1B.

FIG. 1A and FIG. 1B illustrate only two DI water sources, two sourcespipes, and two flow control devices for convenience and simplificationof explanation, and embodiments of the present disclosure are notlimited thereto. Embodiments of more than two DI water sources, morethan two sources pipes, and more than two flow control devices aredescribed hereinafter.

Referring to FIG. 1C, FIG. 1C illustrates a schematic view showing asystem for providing DI water with a dynamic electrical resistivity inaccordance with alternative embodiments of the present disclosure. Asshown in FIG. 1C, a system 100′ includes DI water sources 110C, 110D,110E and more, source pipes 120C, 120D, 120E and more, flow controldevices 130C, 130D, 130E and more, a merging pipe 140′ and a flowcontroller 150′, which are similar to the DI water sources 110A and110B, the source pipes 120A and 120B, the flow control devices 130A and130B, the merging pipe 140 and the flow controller 150 of FIG. 1A andFIG. 1B. It is noted that the DI water sources 110C, 110D, 110E and moremay have at least three different electrical resistivities in someembodiments. Each of the flow control devices 130C, 130D, 130E and morehas its own rotating angles, for example, the flow control device 130Chas a rotating angle 132C. The rotating angle 132C is defined in asimilar way as the rotating angles 132A and 132B of FIG. 1B and may notbe repeated herein. In addition, the flow controller 150′ includes aresistivity sensor 152′, a driving module 154′ and a judging module156′, which are similar to the resistivity sensor 152, the drivingmodule 154 and the judging module 156 of FIG. 1B. The followingdescribes method for providing DI water with a dynamic electricalresistivity using the systems 100 and 100′, respectively.

FIG. 2A and FIG. 2B are used to describe a method 200 for providing DIwater with a dynamic electrical resistivity in accordance with someembodiments of the present disclosure. FIG. 1C is also incorporated,however, the following uses only the DI water sources 110C, 110D and110E, the source pipes 120C, 120D and 120E, and the flow control devices130C, 130D and 130E to represent plural DI water sources, source pipesand flow control devices of FIG. 1C for convenience of explanation.Please refer to FIG. 2A and FIG. 1C. FIG. 2A illustrates a flow chartshowing the method 200 for providing DI water with a dynamic electricalresistivity. As shown in operation 210 in FIG. 2A, a system forsupplying DI water with different electrical resistivities is providedfirst, for example , the system 100′ of FIG. 1C. The system may includethe merging pipe 140′ joining the source pipes 120C, 120D and 120E thatare respectively connected to DI water sources 110C, 110D and 110E in aone-to-one manner, in which the DI water sources 110C, 110D and 110Erespectively have different electrical resistivities R₁, R₂ and R₃, andthe flow control devices 130C, 130D and 130E are respectively disposedin the source pipes 120C, 120D and 120E in a one-to-one manner. That is,a number of the source pipes, DI water sources and the flow controldevices may be the same. In some embodiments, the flow control devicesmentioned in FIG. 2A may be a flow control valve. In other embodiments,the flow control devices 130C, 130D and 130E may be dampers, and each ofthe dampers has its own rotating angle (e.g. the rotating angle 132C ofthe damper 130C). Each rotating angle is in a range substantially from0° to 90°, and at least one of the rotating angles is not 0°. Forsimplifying the descriptions, the following takes the dampers 130C, 130Dand 130E as an example of the flow control devices 130C, 130D and 130E,while the example is not intended to limit the scope of the presentdisclosure.

At operation 220, the dampers 130C, 130D and 130E are initialized tosupply DI water from the system. Initializing the dampers 130C, 130D and130E is aimed at setting an initial state of the dampers 130C, 130D and130E that is easier to obtain DI water having a target electricalresistivity or close to the target electrical resistivity, in which theinitial state may be referred as the rotating angles of the dampers130C, 130D and 130E to perform the control operation (which will bedescribed later at operation 230). To be initialized, the dampers 130C,130D and 130E may be also signally connected to a driving module 154′.

The initial state may be automatically calculated by the calculatingmodule 160′ in some embodiments. In such embodiments, the calculatingmodule 160′ may be signally connected to the driving module 154′ of theflow controller 150′, so as to transfer the calculation results to thedriving module 154′. For example, the initial state may be achieved byadjusting the rotating angles of the dampers 130C, 130D and 130E, inwhich the initial state (i.e. the rotating angles) may be calculated bythe above relationship (1). For example, the rotating angles of theinitial state may be calculated by R (target electricalresistivity)=(R₁A₁+R₂A₂+R₃A₃)/(A₁+A₂+A₃), and then the dampers 130C,130D and 130E may be adjusted by the driving module 154′ according tothe calculation results. However, the initial state may be manuallydetermined in other embodiments. In some embodiments, the targetelectrical resistivity may be in a range from a highest electricalresistivity to a lowest electrical resistivity of the DI water in the DIwater sources 110C, 110D and 110E.

Next, as shown in operation 230, a control operation is performed by aflow controller 150′. FIG. 2B illustrates a flow chart showing thecontrol operation 230 in the method 200 in accordance with someembodiments of the present disclosure. As shown in FIG. 2B, the controloperation 230 includes operations 232, 234 and 236 or 238 in someembodiments of the present disclosure. At operation 232, an actualelectrical resistivity of DI water in the merging pipe 140′ is detected.In some embodiments, the actual electrical resistivity may be detectedby a resistivity sensor 152′ disposed in the merging pipe 140′.

Then, at operation 234, a judgement is performed to determine whetherthe actual electrical resistivity is equal to the target electricalresistivity or not. Determining the actual electrical resistivity may beperformed by a judging module 156′ of the flow contro11er 150′. Forexample, the target electrical resistivity may be setup in the judgingmodule 156′ before the control operation 230 starts, and then the actualelectrical resistivity is detected (as shown in operation 232) andsignally transferred from the resistivity sensor 152′ to the judgingmodule 156′ to perform operation 234. Accordingly, the resistivitysensor 152′ and the judging module 156′ are signally connected to eachother, and the judging module 156′ is able to receive a signal from theresistivity sensor 152′. It is noted that the target electricalresistivity may be predetermined based on a requirement of thesemiconductor fabricating process. Therefore, the target electricalresistivity of the present disclosure does not limited to a fixed value.

Next, based on the judgement of operation 234, operation 236 oroperation 238 is performed. Therefore, the driving unit 154′ is at leastsignally connected to the judging module 156′, so as to receive a signalfrom the judging module 156′. In some embodiments, when the actualelectrical resistivity is equal to the target electrical resistivity(R_(A)≠R_(T), referred as “Y” in FIG. 2B), as shown in operation 236,the DI water in the merging pipe may be applied to the semiconductorfabricating process. In other embodiments, when the actual electricalresistivity is not equal to the target electrical resistivity(R_(A)≠R_(T), referred as “N” in FIG. 2B), the flowrates through thesource pipes 120A and 120B are adjusted by adjusting the rotating angleof the dampers 130C, 130D and 130E to supply water again for repeatingthe control operation 230, as shown in operation 238. In someembodiments, the rotating angles may be stepwise adjusted (increased ordecreased) by the driving module 154′ of the flow controller 150′. Theterm of “stepwise” refers to adjusting the rotating angles by increasingor decreasing a fixed angle at one time. For example, the fixed anglemay be 0.5°, 1°, 5° or any other suitable angles. In other embodiments,when the flow control devices 150′ are flow control valve (not shown),the degree of openings of the flow control valves may be adjusted toachieve desired flowrate.

In some embodiments, a feedback loop may be established. That is, theactual electrical resistivity is detected (operation 232), followed bythe judgement of the actual electrical resistivity (operation 234) andthe adjustment of the rotating angles (238), and the actual electricalresistivity of the DI water is detected again (operation 232) after therotating angles are adjusted.

An embodiment using two DI water sources respectively having a high anda low electrical resistivity is shown to further illustrate theapplication of the method of the present disclosure. Referring to FIG.3A and FIG. 3B, a flow chart of a method 300 for providing DI waterhaving a dynamic electrical resistivity is provided in accordance withsome embodiments of the present disclosure. FIG. 1B is also incorporatedfor clear explanation. As shown in operation 310 of FIG. 3A, a systemsuch as the system 100 of FIG. 1B is provided. Furthermore, a diameterof the source pipes 120A and 120B (or so called a first source pipe anda second source pipe) may be the same in the embodiments described here.In the embodiments described in FIG. 3A and FIG. 3B, the DI watersources 110A and 110B respectively have a high and a low electricalresistivity.

At operation 320, the first and second rotating angles 132A and 132B areinitialized according to the following relationship (2):

$\begin{matrix}{{R^{\prime}\left( {M\; {\Omega \cdot {cm}}} \right)} = \frac{{X \times A\; 1} + {Y \times A\; 2}}{{A\; 1} + {A\; 2}}} & (2)\end{matrix}$

where R′ stands for the target electrical resistivity; X stands for thehigh electrical resistivity; Y stands for the low electricalresistivity; A1 stands for the first rotating angle 132A; and A2 standsfor the second rotating angle 132B. In some embodiments, the first andsecond rotating angles 132A and 132B may be in a range substantiallyfrom 0° to 90°, and at least one of the first and second rotating angles132A and 132B is not 0°. For example, the high electrical resistivity Xmay be 24 MΩ·cm and the low electrical resistivity Y may be 12 MΩ·cm.When the target electrical resistivity is set to be 18 MΩ·cm, therotating angles A1 and A2 may be the same, for example, both therotating angles A1 and A2 may be initialized to 45°. In someembodiments, initializing the first and second rotating angles 132A and132B is performed by a similar method mentioned in operation 220 of FIG.2A and may not be repeated herein.

At control operation 330, a control operation is performed. FIG. 3Billustrates a flowchart showing the control operation 330 in accordancewith some embodiments of the present disclosure. At operation 331, anactual electrical resistivity of the DI water in the merging pipe 140 isdetected, in which operation 331 of FIG. 3B is similar to operation 232Aof FIG. 2B and may not be repeated herein. Then, as shown in operation333, a judgement is performed to determine whether the actual electricalresistivity (R_(A)) is substantially equal to the target electricalresistivity (R_(T)). Operation 333 of FIG. 3B is similar to operation234A of FIG. 2B and may not be repeated herein.

Then, one of operation 332, operation 334 and operation 336 is performeddepending on the judgement of operation 333. The following describes indetailed. It is noted that, although the rotating angles are initiatedto theoretical values for obtaining the DI water having the targetelectrical resistivity, the actual situation (e.g. precision of theflowrate of the DI water sources, a change in diameters of the pipes,etc.) of the DI water sources and the source pipes may further affectthe actual electrical resistivity. Therefore, detecting and adjustingoperations are required to make the actual electrical resistivity moreprecise and closer to the target electrical resistivity.

In some embodiments, when the actual electrical resistivity issubstantially equal to the target electrical resistivity (R_(A)=R_(T)),the DI water may be applied to the semiconductor fabricating process, asshown in operation 332.

In some embodiments, when the actual electrical resistivity is smallerthan the target electrical resistivity (R_(A)<R_(T)), the first rotatingangle 132A may be increased and/or the second rotating angle 132B may bedecreased, so as to increase a percentage of the DI water having thehigh electrical resistivity, and/or decrease a percentage of the DIwater having the low electrical resistivity, as shown in operation 334of FIG. 3B. Therefore, the actual electrical resistivity may becomecloser to the target electrical resistivity. As shown in FIG. 3B, thecontrol operation 330 may be repeated from operation 331 after operation334 is performed. The control operation 330 may be repeated till theactual electrical resistivity is substantially equal to the targetelectrical resistivity (R_(A)=R_(T)). In some embodiments, the first andsecond rotating angles 132A and 132B may be adjusted by a similarstepwise method mentioned in operation 236A of FIG. 2B and may not berepeated herein.

In some embodiments, when the actual electrical resistivity is greaterthan the target electrical resistivity (R_(A)>R_(T)), the first rotatingangle 132A may be decreased and/or the second rotating angle 132B may beincreased, so as to decrease a percentage of the DI water having thehigh electrical resistivity, and/or increase a percentage of the DIwater having the low electrical resistivity, as shown in operation 336of FIG. 3B. Therefore, the actual electrical resistivity may becomecloser to the target electrical resistivity. As shown in FIG. 3B, thecontrol operation 330 may be repeated from operation 331 after operation336 is performed. The control operation 330 may be repeated till theactual electrical resistivity is substantially equal to the targetelectrical resistivity (R_(A)=R_(T)). In some embodiments, the first andsecond rotating angles 132A and 132B may be adjusted by a similarstepwise method mentioned in operation 236A of FIG. 2B and may not berepeated herein.

The system and the method for providing DI water with a dynamicelectrical resistivity of the present disclosure may automatically anddynamically adjust the electrical resistivity of DI water in real-timeby a feedback loop. DI water having a target electrical resistivity maybe easily and precisely obtained. Therefore, the same system may beapplied to various semiconductor fabricating processes, and the systemand the method of the present disclosure effectively reduceelectrostatic charges accumulated on the surface of the wafer duringdifferent semiconductor fabricating processes. Accordingly, the systemand the method of the present disclosure advantageously provide meritssuch as low costs, simplification and high performance.

According to some embodiments of the present disclosure, a methodincludes mixing a first deionized water (DI) water from a first pipe anda second DI water from a second pipe in a merging pipe that is in fluidcommunication with the first pipe and the second pipe. An electricalresistivity of the first DI water is different from an electricalresistivity of the second DI water. A mixture of the first DI water andthe second DI water is applied from the merging pipe onto a wafer.

According to some embodiments of the present disclosure, a methodincludes mixing a first deionized water (DI) water from a first pipe anda second DI water from a second pipe in a merging pipe that is in fluidcommunication with the first pipe and the second pipe. An electricalresistivity of the first DI water is higher than an electricalresistivity of the second DI water. An electrical resistivity of amixture of the first DI water and the second DI water is measured. Aflow rate of the first DI water through the first pipe is adjustedaccording to the measured electrical resistivity of the mixture of thefirst DI water and the second DI water.

According to some embodiments of the present disclosure, a methodincludes calculating a first angle for a first flow control device in afirst pipe according to an electrical resistivity of a first deionizedwater (DI) water in the first pipe, an electrical resistivity of asecond DI water in a second pipe, and a target electrical resistivity.The electrical resistivity of the first DI water is different from theelectrical resistivity of the second DI water. The first angle isrelative to a close position of the first flow control device. The firstflow control device is rotated to the calculated first angle. The firstDI water from the first pipe and the second DI water from the secondpipe are mixed in a merging pipe that is in fluid communication with thefirst pipe and the second pipe.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method, comprising: mixing a first deionizedwater (DI) water from a first pipe and a second DI water from a secondpipe in a merging pipe that is in fluid communication with the firstpipe and the second pipe, wherein an electrical resistivity of the firstDI water is different from an electrical resistivity of the second DIwater; and applying a mixture of the first DI water and the second DIwater from the merging pipe onto a wafer.
 2. The method of claim 1,further comprising: measuring an electrical resistivity of the mixtureof the first DI water and the second DI water.
 3. The method of claim 2,wherein the electrical resistivity of the mixture of the first DI waterand the second DI water are measured in the merging pipe.
 4. The methodof claim 2, further comprising: adjusting a flow rate of the first DIwater through the first pipe according to the measured electricalresistivity of the mixture of the first DI water and the second DIwater.
 5. The method of claim 4, further comprising: adjusting a flowrate of the second DI water through the second pipe according to themeasured electrical resistivity of the mixture of the first DI water andthe second DI water.
 6. The method of claim 1, further comprising:mixing a third DI water from a third pipe with the first DI water andthe second DI water.
 7. The method of claim 6, wherein an electricalresistivity of the third DI water is different from the electricalresistivity of the first DI water and the electrical resistivity of thesecond DI water.
 8. A method, comprising: mixing a first deionized water(DI) water from a first pipe and a second DI water from a second pipe ina merging pipe that is in fluid communication with the first pipe andthe second pipe, wherein an electrical resistivity of the first DI wateris higher than an electrical resistivity of the second DI water;measuring an electrical resistivity of a mixture of the first DI waterand the second DI water; and adjusting a flow rate of the first DI waterthrough the first pipe according to the measured electrical resistivityof the mixture of the first DI water and the second DI water.
 9. Themethod of claim 8, wherein adjusting the flow rate of the first DI waterthrough the first pipe comprises: increasing an angle of a first flowcontrol device in the first pipe when the measured electricalresistivity of the mixture of the first DI water and the second DI wateris lower than a target electrical resistivity, wherein the angle of thefirst flow control device is relative to a close position of the firstflow control device.
 10. The method of claim 8, further comprising:increasing an angle of a second flow control device in the second pipewhen the measured electrical resistivity of the mixture of the first DIwater and the second DI water is higher than a target electricalresistivity, wherein the angle of the second flow control device isrelative to a close position of the second flow control device.
 11. Themethod of claim 8, further comprising: applying the mixture of the firstDI water and the second DI water from the merging pipe onto a wafer whenthe measured electrical resistivity of the mixture of the first DI waterand the second DI water is substantially equal to a target electricalresistivity.
 12. The method of claim 11, wherein the target electricalresistivity is between the electrical resistivity of the first DI waterand the electrical resistivity of the second DI water.
 13. The method ofclaim 8, further comprising: calculating a first angle for a first flowcontrol device in the first pipe according to the electrical resistivityof the first DI water, the electrical resistivity of the second DIwater, and a target electrical resistivity, wherein the first angle isrelative to a close position of the first flow control device; androtating the first flow control device to the calculated first angle.14. The method of claim 13, further comprising: calculating a secondangle for a second flow control device in the second pipe according tothe electrical resistivity of the first DI water, the electricalresistivity of the second DI water, and the target electricalresistivity, wherein the second angle is relative to a close position ofthe second flow control device; and rotating the second flow controldevice to the calculated second angle.
 15. A method, comprising:calculating a first angle for a first flow control device in a firstpipe according to an electrical resistivity of a first deionized water(DI) water in the first pipe, an electrical resistivity of a second DIwater in a second pipe, and a target electrical resistivity, wherein theelectrical resistivity of the first DI water is different from theelectrical resistivity of the second DI water, and the first angle isrelative to a close position of the first flow control device; rotatingthe first flow control device to the calculated first angle; and mixingthe first DI water from the first pipe and the second DI water from thesecond pipe in a merging pipe that is in fluid communication with thefirst pipe and the second pipe.
 16. The method of claim 15, furthercomprising: calculating a second angle for a second flow control devicein the second pipe according to the electrical resistivity of the firstDI water, the electrical resistivity of the second DI water, and thetarget electrical resistivity, wherein the second angle is relative to aclose position of the second flow control device; and rotating thesecond flow control device to the calculated second angle.
 17. Themethod of claim 15, wherein the first pipe and the second pipe havesubstantially the same diameter.
 18. The method of claim 15, furthercomprising: measuring an electrical resistivity of a mixture of thefirst DI water and the second DI water after rotating the first flowcontrol device to the calculated first angle.
 19. The method of claim18, further comprising: adjusting an angle of the first flow controldevice in the first pipe according to the measured electricalresistivity of the mixture of the first DI water and the second DIwater.
 20. The method of claim 19, further comprising: adjusting anangle of a second flow control device in the second pipe according tothe measured electrical resistivity of the mixture of the first DI waterand the second DI water.